Food allergy is a prevalent disorder associated with significant morbidity and mortality. There are currently no effective preventive measures or cures and tools for diagnosis are imperfect. This situation calls for innovative strategies to precisely define the molecular and cellular pathways in food allergy both so that novel diagnostic markers predicting risk of allergic reaction can be identified and so that new candidate targets for therapy can be identified. The known associations of several atopic conditions with activating polymorphisms in components of IL-4/13 receptors, along with our preliminary observation of intense food anaphylaxis in mice harboring an activating variant of IL-4R, provide support for our central hypothesis: that IL-4 signaling is critical in food anaphylaxi, driving TH2 responses, mast cell expansion and suppression of Treg. F709 mice, in which the inhibitory cytosolic ITIM motif of IL-4R is disrupted, will be used to test the hypothesis. Unlike their wild-type Y709 counterparts which are tolerant to dietary antigens, they develop robust IgE responses to ingested proteins, intestinal mast cell expansion and full-blown anaphylactic reactions upon enteral challenge. This phenotype is unique among murine food allergy models, closely mimicking food allergy in humans. The F709 system provides a powerful resource both for focused analysis of direct IL-4 effects on mast cells T cells and intestinal epithelium and for probing the interactions between mast cells, IgE antibodies, TH2 and Treg cells in the development of food allergy. Our hypothesis will be tested with the following aims: AIM 1: To define effects of enhanced IL-4 signaling on mast cell responsiveness, protease phenotype, gene expression and homeostasis in food allergy and to test IL-4R effects on target tissue sensitivity to mediators and on intestinal permeability AIM 2: To test mast cell and IgE antibody effects on immune sensitization (humoral and TH2responses) and on regulatory T cell (Treg) induction in F709 mice AIM 3: To examine the effects of pharmacologic mast cell inhibition or IgE blockade on immune sensitization to food allergens and on regulation of established responses Anticipated outcome: By defining specific alterations in mechanisms of mast cell, T cell, target tissue and gut epithelial functions in food allergen responses occurring in the settin of enhanced IL-4 signals, these studies will establish the critical factors, in addition to specifi IgE production, that place individuals at risk for food anaphylaxis. This has the potential to lead to both novel diagnostic markers for food allergy and to the identification of candidate targets fo therapy in established food allergy.